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      function fn() {
        let num = 10
        function fun() {
          console.log(num)
          return 'aa'
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        // a1
        return fun
      }
      // fn()
      console.log('fn()()', fn()())
      console.log('(fn())()', (fn())())
      console.log('fn()',fn())

      // a2
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      f()
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